<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Custom Resize Handler</title>
    <style>
        .column {
            overflow: hidden;
        }
        .column-left {
            height: 400px;
            background-color: #fff;
            position: relative;
            float: left;
        }
        .column-right {
            height: 400px;
            padding: 16px;
            background-color: #eee;
            box-sizing: border-box;
            overflow: hidden;
        }
        .resize-save {
            position: absolute;
            top: 0; right: 5px; bottom: 0; left: 0;
            padding: 16px;
            overflow-x: hidden;
        }
        .resize-bar {
            width: 200px; height: inherit;
            resize: horizontal;
            cursor: ew-resize;
            opacity: 0;
            overflow: scroll;
        }
        /* 拖拽线 */
        .resize-line {
            position: absolute;
            right: 0; top: 0; bottom: 0;
            border-left: 5px solid #bbb;
            pointer-events: none;
        }
        .resize-bar:hover ~ .resize-line,
        .resize-bar:active ~ .resize-line {
            border-left: 5px dashed skyblue;
        }
        .resize-bar::-webkit-scrollbar {
            width: 200px; height: inherit;
        }

        /* Firefox只有下面一小块区域可以拉伸 */
        @supports (-moz-user-select: none) {
            .resize-bar:hover ~ .resize-line,
            .resize-bar:active ~ .resize-line {
                border-left: 1px solid #bbb;
            }
            .resize-bar:hover ~ .resize-line::after,
            .resize-bar:active ~ .resize-line::after {
                content: '';
                position: absolute;
                width: 16px; height: 16px;
                bottom: 0; right: -8px;
                background: url(./resize.svg);
                background-size: 100% 100%;
            }
        }
    </style>
</head>
<body>
<div class="column">
    <div class="column-left">
        <div class="resize-bar"></div>
        <div class="resize-line"></div>
        <div class="resize-save">
            左侧的内容，左侧的内容，左侧的内容，左侧的内容
        </div>
    </div>
    <div class="column-right">
        右侧的内容，右侧的内容，右侧的内容，右侧的内容
    </div>
</div>
</body>
</html>